Despite the promise of CVD-grown graphene for technology, this growth technique tends to yield samples with more defects, such as carbon vacancies and domain boundaries, compared to exfoliated graphene [1]}. Here, we present an unexpected characteristic of those defects, with implications for any technology that relies on spin or quantum coherence. We show that a typical annealing process used to remove residues from graphene devices [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]} significantly enhances the quantum mechanical phase-breaking (dephasing) rate measured via weak localization (WL)[9]}. Although data from phase coherent measurements at cryogenic temperatures might seem unrelated to applications at room temperature, our results suggest that these activated defects create a fast mechanism for spin relaxation that would limit the use of CVD graphene in spintronics. At the same time, this finding sheds light on the microscopic origin of local moments in this form of graphene, which may help to devise growth recipes to avoid them in the first place.
